1. Field of the Invention
The present invention relates to textile technologies, and more particularly to methods and apparatus for testing snarling properties of yarns or the like.
2. Background of the Invention
In almost all types of spun yarns there exists some residual torque, which makes these yarns prone to snarling. Snarls are formed when two ends of a twist lively yarn are brought together. Yarn snarling has a significant influence on the processing behavior and performance characteristics of yarns and fabrics. In textile technological processes snarling caused by residual torque is considered as a serious problem leading to yarn breakage, deterioration of yarn properties and equipment malfunction. Fabric characteristics such as spirality of knitted fabrics and skewness of woven fabrics are also dependent on the level of residual torque in a yarn. Thus the measurement of yarn residual torque is particularly important.
Despite its importance as a yarn quality parameter, the measurement of yarn residual torque is actually rarely used to characterize a twisted yarn.
Although there has never been a generally available standard instrument for measuring the torsional characteristics of textile fibers or yarns, various methods and apparatus have been developed and can be divided into three categories, namely direct, semi-direct or indirect measurements.
Two experimental techniques to measure yarn torque by using the direct method, namely torsion pendulum and torsion balance techniques have been reported by Dhingra and Postle in the Journal of the Textile Institute, Vol. 65, 1974. According to Dhingra and Postle, the torsion pendulum technique is simple and rapid and does not require any elaborate apparatus but the information provided is severely limited in that the rigidity is measured for only small strains, imposed for a short period of time. This technique is not suitable for investigation of the torsional behavior of twisted yarns owing to the untwisting tendency of the lower end of the yarn. The torsion balance technique involves attaching one end of a twist lively yarn of specified length to a torsion disc, with the other end fixed. The torsion disc is attached to a torsion wire of known torsional stiffness. A pointer or similar indicating device is positioned between the specimen and the torsion wire. As the specimen is twisted, the torsion wire head is rotated manually so as to maintain the pointer freely in a constant position or, alternatively, the head may be fixed and the torque measured by the rotation of the indication device.
In the Journal of the Textile Institute, Vol. 4, 1979 Bennett et al used a torsion balance to experimentally measure yarn torque to investigate the torque-twist and recovery characteristics of continuous-filament and staple-fiber yarns. A torsional apparatus has been described by Noor in Textile Asia, No. 11, 1993. The apparatus consists of a twisting unit, a torque-measuring unit, a contraction measuring unit and associated data recording devices. Morton and Permanyer in the Journal of the Textile Institute, Vol. 38, 1947 disclosed the details of a device to measure the torsional rigidity of textile fibers called a Torsiometer. The Torsiometer consists of three parts arranged in vertical alignment: at the top a measuring head; at the bottom a twisting unit; and between them a rigid connecting link carrying an equilibrium pointer.
Tavanai et al reported a semi-direct method to measure yarn-torque level in the Journal of the Textile Institute, Vol. 87, 1996 called the Torquemeter. The method involves free rotation of a disc “attached to one end of a vertically suspended twist-lively yarn, with the upper end fixed, the disc will rotate and oscillate back and forth until it finally comes to rest.” The system to evaluate the twist liveliness can be measured by one of two approaches: the first one being the total number of turns of twist change by the difference between the sum of forward and backward rotations A second approach disclosed by Berndt et al in Melliand Textilberichte, No. 65, 1984 uses a specially designed disc containing holes arranged in a binary pattern “which allows infra red senders and receivers to detect the direction of yarn twist liveliness and the number and rate of yarn and disc rotation. The torque in the yarn can be computed from the oscillation data and other constants, such as disc inertia.”
The indirect method as described in the ISO Standard 03343-1984, is one of the simplest ways to obtain an idea about the residual torque in yarns by counting the number of snarls in a 1 m yarn segment with the two ends completely in contact. Based on the principle that a yarn containing residual torque will tend to snarl, several attempts have been made to develop a method to measure yarn snarliness. These methods usually involve suspending a light object from the middle of a known length of yarn. As soon as the two ends are brought together, snarls are formed. The number of turns or the distance between the two yarn ends when a snarl begins to form gives the snarliness level. Primentas disclosed the details of a device for testing yarn snarliness called ‘Prianic’ in The Indian Textile Journal, Vol. 28 No. 3, 2003. However, the method of measuring the twist liveliness by measuring the distance when a snarl begins to form can be, in practice, difficult to determine the exact point of snarling if the yarn is very twist lively.
Although a number of direct, semi direct and indirect methods of yarn residual torque evaluation exists, the most accurate method can be considered to be the direct approach. However this method may not be industrially practical since that elaborate and complex apparatus is required and that the results obtained by different authors are not easily comparable because of the different types of apparatus used and the different conditions under which the experiments were performed.